The Malewa River rises in the western slopes of the Aberdare Range in Kenya and flows south and west into Lake Naivasha in the Great Rift Valley.

Lake Naivasha is an important source of water in a semi-arid environment, and supports export-oriented horticulture and floriculture businesses as well as tourism.

[1] The headwaters of the main channel of the Malewa originate at an elevation of 3,700 metres (12,100 ft) in the Nyandarua (Aberdare) mountains.

The highlands drained by the Malewa are volcanic and contribute sodium and calcium to the water through chemical weathering of the rocks.

[7] The river is threatened by deforestation and siltation, increasing diversion of water for irrigation, and pollution by fertilizers and pesticides.

[8] In August 1997 sediment-laden plumes of Malewa river water extended about 500 metres (1,600 ft) into Lake Naivasha.